As this type of ultrasonic flowmeter, an ultrasonic flowmeter is known that has an ultrasonic transceiver on each of the outer periphery upstream of a pipe and the outer periphery downstream of the pipe, measures the propagation time by propagating an ultrasonic wave in the flow direction of a fluid and the propagation time by propagating an ultrasonic wave in the opposite direction, and calculates the flow velocity of the fluid based on the propagation times. In this type of flowmeter, an ultrasonic wave emitted from a transmitter reaches a receiver as a fluid propagation wave propagating in the fluid and reaching the receiver and a pipe propagation wave propagating in the pipe wall and reaching the receiver. The fluid propagation wave is a signal component required for measurement and the pipe propagation wave is a noise component superimposed on the signal component.
For attenuation of this noise component, a damping material (ultrasonic absorber) for attenuating the energy of the pipe propagation wave is formed cylindrically on the outer wall of the pipe between two ultrasonic transceivers to improve the S/N ratio (signal-to-noise ratio). For example, PTL 1 discloses an example of an ultrasonic flowmeter provided with a damping material on the pipe.